The invention relates to the field of waveguide-to-semiconductor coupling devices, and in particular a waveguide-to-semiconductor device having waveguide/semiconductor interface structures with Brewster angles for TM modes and multimode interferometer (MMI) structures at a waveguide end for TE modes.
The low efficiency in waveguide-to-semiconductor coupling devices is a serious problem in photonics chips. A majority of waveguides are comprised of low index materials (SiNx: 2.2, SiOxNy: 1.5), while other standard semiconductor devices, such as detectors, modulators, emitter, and amplifier are comprised of high index structures (Ge: 4.2, Si:3.5, GaAs: 3.6). One example of inefficient coupling is between a Ge detector and waveguide. Approximately 40% of incident light is reflected between Ge and SiNx causing significant Fresnel loss. In most photonic applications, this amount of loss is unacceptable and very inefficient. In evanescent coupling the propagation velocity mismatch between the waveguide and Ge detector needs a long coupling length. A long coupling length would be inefficient in photonic applications because size is an essential factor that needs to be controlled for such applications to operate efficiently with minimum loss.